Three-Dimensional Simulations of Classical Novae

TL;DR

This paper presents 3D simulations of classical novae on white dwarfs, revealing different flow patterns from 2D models and showing that rapid outbursts require significant pre-enrichment of C and O in the accreted material.

Contribution

First 3D hydrodynamic simulations of nova explosions demonstrating the importance of initial composition for outburst speed.

Findings

Flow patterns differ significantly from 2D simulations.

Self-enrichment of accreted hydrogen is too slow for rapid outbursts.

Fast novae require pre-existing C and O enrichment.

Abstract

We present first results of three-dimensional (3D-) calculations of turbulent and degenerate hydrogen-burning on top of a C+O white dwarf of one solar mass. The simulations are carried out by means of a code which solves Euler's equation for an arbitrary equation of state together with a nuclear reaction network and the energy input from nuclear reactions on a Cartesian grid covering a fraction of the white dwarf's surface and accreted atmosphere. The flow patterns we obtain are very different from those of earlier 2D simulations using the same initial conditions and the same numerical resolution. The possibility of self-enrichment of the accreted hydrogen-rich atmosphere with carbon and oxygen from the surface layers of the white dwarf during the violent phase of the burning is investigated, and it is demonstrated that self-enrichment proceeds too slowly if the accreted gas has near-solar CNO-abundances at the onset of the thermonuclear runaway. As a result, we do not find a fast nova outburst. This conclusion remains valid if the initial metallicity of the accreted gas is raised by a factor of five. Therefore we conclude that fast nova outbursts indeed require huge enrichments of C and O, as postulated from spherically symmetric models, and that the mechanism which leads to such enhancements must operate prior to the outburst.